Marine propulsion systems generally operate to move a vessel in water by producing an accelerated column of water acting against the vessel. The column of water, known as the slipstream, provides a thrust against the propeller, nozzle or other propulsive device to push the vessel through the water.
The present invention, generally, provides an apparatus for increasing the thrust of a marine propulsion system without increasing the load on the engine.
More particularly, the present invention provides an apparatus for increasing the thrust of a conventional marine propulsion system by providing a blanket or layer of air surrounding a slipstream produced by a propulsion system.
According to a first embodiment, the invention provides a device for a propeller. The propeller apparatus comprises a cowling for a conventional marine propeller that radially encloses a propeller and extends downstream of the propeller to encircle the slipstream of the propeller. An inner part of the cowling is shaped as a section of a cone, with the propeller disposed in a front end of the cone section, and the cone section axially converging (or narrowing) in the rearward direction. An outer pan of the cowling is tubular shaped and is longer than the inner part. A front end of the outer part is joined with a front end of the inner part so that the inner and outer parts form a rearward opening annular chamber. Means for providing air to the annular chamber is included to form a blanket of air around the propeller slipstream.
The means for providing air comprises at least a conduit leading engine exhaust to the annular chamber. Additional means includes a duct to lead ambient air to the annular chamber. Movement of the slipstream causes a vacuum in the annular chamber that draws air through the ambient air duct. Other suitable means may also be provided.
A second embodiment relates to bow and stern thrusters for producing lateral movement of a vessel, for example, for maneuvering the vessel during docking. According to the invention, a bow or stern thruster apparatus includes a first pipe connected to a thrust producing device and directed toward a hull of the vessel. A second pipe, having an inner diameter greater than an outer diameter of the first pipe is connected to the hull to form an outlet. The first pipe is disposed in the second pipe so that a space surrounds the first pipe.
The second pipe is connected to a duct for carrying outside air to the space around the first pipe. An outlet of the first pipe is spaced from the outlet of the second pipe and the hull, which provides an exhaust duct for the water stream exiting the first pipe. The exhaust duct provides the part of the apparatus where a blanket of air forms around the stream of water exiting the outlet of the first pipe. Air will typically be aspirated into and through the air duct by the movement of the water stream. Alternatively, air may be forced through the duct by suitable means.